Mass spectrum single compound

How then are these ions/decompositions chosen Before considering this we must define, very carefully, the requirements of the analysis to be carried out. Is a single compound to be determined or are a number of compounds of interest If a single compound is involved, its mass spectrum and MS-MS spectra can be obtained and scrutinized for any appropriate ions or decompositions. If the requirement is to determine a number of analytes, their chromatographic properties need to be considered. If they are well separated, different ions/decompositions can be monitored for discrete time-periods as each compound elutes, thus obtaining the maximum sensitivity for each analyte. If the analytes are not well separated, this approach may not be possible and it may then be necessary to monitor a number of ions/decompositions for the complete duration of the analysis. If this is the case, the analyst should attempt to find the smallest number of ions/decompositions that give adequate performance for all of the analytes (remember the more ions/decompositions monitored, then the lower the overall sensitivity will be). 

Example ESI selectively ionizes the basic compounds, i.e., only a small fraction of the entire chemical composition, in a sample of South American cmde oil. Nevertheless, the positive-ion ESI-FT-ICR mass spectrum exhibits more than 11,100 resolved peaks, of which >75 % may be assigned to a unique elemental composition (CcHhOoNnSJ. Such a separation in mass is possible because the average mass resolution in the m/z 225-1000 broadband spectrum is approximately 350,000 (Fig. 12.12). This demonstrates the current upper limit for the number of chemically distinct components resolved and identified in a single step. [86]... 

A potential limitation in the application of MS to near-surface measurements is the tremendous number of compounds in the atmosphere, particularly organics, and hence the increased complexity of interpretation of the single mass spectrum. In the MS ion source, the use of particular ion-molecule reactions to form the ions of interest or the ionization of one selected com-... 

Dimethyl bromosuccinate was prepared from bromosuccinic acid by the diazomethane method (26) using the procedure of Eisenbraun, Morris, and Adolphen (27). It was distilled under vacuum (0.08-0.1 Torr) at 45°-49°C to yield a clear colorless oil. Thin layer chromatography with benzene as the solvent on SiC>2 yielded a symmetrical single spot, indicating either a pure compound or no separation with this particular solvent. Its mass spectrum had a very small peak corresponding to the parent compound, but none to a dibromo compound. The mass spectrum for dimethyl bromosuccinate was not found in the literature, but that for dimethyl succinate also has a small peak corresponding to the parent compound (25). 

While D41 decomposes rather continuously in three equidistant steps, G2 shows two early steps of mass loss which are followed by a longer period of stagnation followed by a third step. With the help of the mass spectrum the single steps can be attributed to different events within the decomposition process. The first two steps are caused by the loss of water, obviously evaporated from two different sites of the solid, which explains the separated steps, both more than 150°C above the boiling point of water. The first loss of water may be due to the small amount of water which is enclosed in the inner spheres of the solid whereas at 400°C the leaving of crystal water is observed, which had obviously been in strong interaction with the inorganic compound. 

Exercise 9-51 A certain halogen compound gave a mass spectrum with molecular ion peaks at m/e 136 and 138 in about equal intensities. The nmr spectrum of this compound gave only a single resonance around 1.2 ppm. What is the structure of the compound Give your reasoning. 

Isotope dilution mass spectrometry is a powerful method for determining the quantity of an element or an associated compound in a sample. It requires that a spike of the same element but with an isotopic composition different from that of the sample be introduced to it in a controlled manner. The mass spectrum of the mixture of spike and sample is then used to determine the concentration of the target element in the original sample. In most cases, a single ratio is used, one that incorporates the major isotope in the spike and the major isotope in the sample these must be different isotopes. The difference in the value of this ratio in the sample and in the mixture of sample and spike is proportional to the amount of the target element in the sample. 

---